1. Field of the Invention
The present invention relates to article carrying apparatuses.
2. Description of the Related Art
Conventionally, various types of article carrying apparatuses for carrying articles such as bulk components while lining them in rows and supplying the articles one at a time have been proposed. Such apparatuses are generally called “feeders,” and various types of feeders exist, including vibration- and belt-type feeders, although vibration-type feeders are the most common. A vibration-type feeder is an apparatus for carrying an article placed on a carry face, which vibrates, by making use of, for example, the phenomenon of relative sliding of the article with respect to the carry face.
One example of such a vibration-type feeder is a linear feeder that carries articles over a straight path. The carrying mechanism of such a linear feeder is described below with reference to FIG. 15A to FIG. 15C.
This feeder is provided with a carry section 410 having a carry face 412a whose carrying direction is linearly restricted, and the carry section 410 vibrates between a second position X2 and a first position X1 set in the front and the rear in the carrying direction (hereinafter, this is also referred to as “reciprocating movement”). As shown in FIG. 15A, when moving toward the forward second position X2 during reciprocating movement, relative sliding of the article W with respect to the carry face 412a is inhibited so that the article W moves together with the carry section 410, whereas as shown in FIG. 15B, when moving toward the rear first position X1, the article W slides relative to the carry face 412a and only the carry section 410 moves to the first position X1 while the article W remains at the forward second position X2. By repeating this reciprocating movement, as shown in FIG. 15C, the article W is fed forward with respect to the carry face 412a in small increments, thereby achieving carrying of the articles.
Methods for controlling the state of this relative sliding include a first method of changing the inertia that acts on the article W itself during reciprocating movement, and a second method of changing the friction that occurs between the article W and the carry face 412a during reciprocating movement.
The first method is achieved by using different acceleration amounts for the forward direction and the backward direction during reciprocating movement of the carry section 410 in the carrying direction. For example, as shown in FIG. 15A, the carry section 410 is moved to the forward second position X2 at as uniform a velocity as possible, thus reducing the rearward inertia that acts on the article W and allowing the article W to move together with the carry section 410 to the second position X2. In contrast, the carry section 410 is moved to the rear first position X1 with a large acceleration (see FIG. 15B), thus causing a large forward inertia to act on the article W that in turn causes the article W to remain at the second position X2 while only the carry section 410 moves to the first position X1.
On the other hand, the second method adds additional vibration, in the normal direction of the carry face 412a, to the carry section 410 (which is hereinafter also referred to as “reciprocating movement”) as it moves back and forth in the carrying direction. For example, as shown in FIG. 15A, when moving to the forward second position X2, the carry section 410 is accelerated upward to increase friction and inhibit relative sliding. Conversely, as shown in FIG. 15B, the carry section 410 is accelerated downward when moving to the rear first position X1 to reduce friction and bring about relative sliding.
Ordinarily, these two methods are combined to effectively control relative sliding and thereby increase the carrying ability of the article carrying apparatus. In other words, the ability to carry the article W is increased by applying, to the carry section 410, vibration having a carrying-direction component in an inertia term and a normal-direction component in a friction term, and further, setting the motion path defining that vibration most suitably for the required specifications, such as the type of the article W to be carried and the carrying capacity.
Expanding upon the above discussion, the problems with such conventional linear feeders are examined below.
FIG. 16A and FIG. 16B respectively show a plan view and a lateral view of a linear feeder of a first conventional example. This feeder 501 is provided with a carry section 510 having a horizontal carry face 512a in which the carrying direction of the article W is in the horizontal direction, plate springs 550 provided on the forward and rear sides in the carrying direction in order to support the carry section 510, and a vibration applying mechanism 520 that causes reciprocating linear motion of the carry section 510 in a direction tilted by a predetermined angle θ with respect to the horizontal direction. Due to this reciprocating linear motion of the carry section 510 between a point A and a point B located obliquely above and forward of point A, an article W that has been placed on the carry face 512a is carried forward in the horizontal carrying direction a little bit at a time.
Here, the reciprocating linear motion direction of the carry section 510 is tilted from the horizontal direction by a predetermined angle θ in order to create vibration components in two directions—these being a carrying-direction component in the inertia term and a normal-direction component in the friction force term—from the unidirectional reciprocating linear motion linking point A and point B. Carrying by relative sliding is thus achieved by appropriately setting a velocity pattern for this unidirectional reciprocating linear motion and appropriately accelerating the carry section 510 in the carrying direction and the normal direction (for example, see JP 2003-40424A (pages 3 to 5, FIGS. 1 to 6)).
However, the motion path of the carry section 510 of the first conventional example is a unidirectional reciprocating linear motion, and thus changing the velocity pattern of the carry section 510 also changes the degree of acceleration in both the carrying direction and the normal direction. Consequently, when setting the velocity pattern, it is possible to give only one of these two directions priority and the other direction has to be ignored. That is, the first conventional example has a poor degree of freedom with regard to setting the motion path of the carry section 510, and it is difficult to achieve a setting at which both the inertia and friction become ideal.
One example of a linear feeder that solves this problem is a feeder 601 according to a second conventional example, which is shown in the lateral view of FIG. 17, with which it is possible to independently set the reciprocating movement in a substantially horizontal direction acting as the carry direction, and the reciprocating movement in the vertical direction acting as the normal direction. The feeder 601 is provided with a carry section 610, a base section 680 that supports the carry section 610 via a plate spring structure 650, and a vibration applying mechanism 620 that is provided in the base section 680 and that applies vibration to the carry section 610.
The plate spring structure 650 is provided with a plate spring 652 that is arranged substantially horizontally and that supports the carry section 610 in such a manner that it can be moved back and forth in the vertical direction, and a plate spring 654 that is disposed vertically and that supports the carry section 610 via the plate spring 652 in such a manner that it can be moved back and forth in the substantially horizontal direction. The vibration applying mechanism 620 is provided with two electromagnets 630 and 660 for adding vibration in the substantially horizontal direction and the vertical direction, and the carry section 610 is provided with two stays 632 and 662 to correspond to these electromagnets 630 and 660. By applying an alternating power to the electromagnets 630 and 660, the carry section 610 is suitably moved back and forth in the vertical direction and the substantially horizontal direction, thereby carrying the article W placed on its carry face 612a forward in the carrying direction (for example, see JP 11-278634A (pages 2 and 3, FIGS. 6 to 8)).
In general, the sinusoidal waveform is the voltage waveform of an alternating power that can be readily used.
However, using a sinusoidal waveform, it is not possible to generate a complex motion path such as one that is asymmetrical with regard to the first half and second half of a single cycle of reciprocating movement. For example, from the standpoint of relative sliding as regards the reciprocating movement in the substantially horizontal direction, it is sufficient in the forward pass to move the carry section at as uniform a velocity as possible and in the return pass to move it in an accelerating manner, but the shape of a sinusoidal waveform is point symmetric with regard to the first half and the second half of a single cycle, and therefore cannot be used to generate such reciprocating movement. Further, creating a voltage waveform having a special shape other than a sinusoidal waveform requires special devices and cannot be performed with ease.
In other words, the feeder 601 of the second conventional example is superior to that of the first conventional example in that the motion path of the carry section 610 can be set independently for both the carrying direction and the normal direction, but the problem of a voltage waveform having a special shape being difficult to obtain cannot be avoided, and thus one cannot say that the feeder 601 has an excellent degree of freedom with regard to setting the motion path of the carry section 610.
Also, using electromagnets 630 and 660 gives rise to the possibility of magnetizing the article W if the article W is magnetic, and this means that there are types of articles W that cannot be carried by the article carrying apparatus 601.
Further, because the carry section 610 is supported by elastic members, such as the plate springs 652 and 654, that have low rigidity, the motion path of the carry face 612a is significantly affected by the elastic deformation of the plate springs 652 and 654. Consequently, there is a possibility that even though the intended motion path may be achieved at portions of the carry face 612a proximate to the stays 632 and 662 to which the motion is input, the motion path may stray from the design with increasing distance in the carrying direction from the stays 632 and 662. This may result in so-called carry nonuniformities, that is, the problem of carrying the article faster or slower depending on the position in the carrying direction, and in extreme cases, there is the possibility that, depending on the position in the carrying direction, the article W may be carried in backwards.